Physical features of the Des Plaines Valley . d physiographic form along the lower Des Plaines demand ex-planation—Among these may be mentioned : The relation of the extinctoutlet to the bed rock, which rises to a considerable height in the bluffsat two places (Lomont and Lockport) : the high level terraces of gravel,conspicuous at several points below Romeo, and terminating near theliearl of the Illinois at Channahon; a lower terrace of rock on both sidesof the valley near Lockport, and the terraces of tributary streams. GOLDTHWAIT. HISTORY OF THE LOWER DES PLAINES. 47 In order to understand
Physical features of the Des Plaines Valley . d physiographic form along the lower Des Plaines demand ex-planation—Among these may be mentioned : The relation of the extinctoutlet to the bed rock, which rises to a considerable height in the bluffsat two places (Lomont and Lockport) : the high level terraces of gravel,conspicuous at several points below Romeo, and terminating near theliearl of the Illinois at Channahon; a lower terrace of rock on both sidesof the valley near Lockport, and the terraces of tributary streams. GOLDTHWAIT. HISTORY OF THE LOWER DES PLAINES. 47 In order to understand the physical features of the valley, we shallfollow the development of successive moraines and outwash depositsalong the retreating ice-border, the formation and the gradual extinc-tion of ice-dammed lakes, and the steps in the cnttiug down of thegreat Chicago outlet. DEPOSITIOX OF THE EARLY WISCONSIN DRIFT. The early Wisconsin moraines.—The outline of the border of theWisconsin ice-sheet in Illinois at the time of its greatest extent is. • Valparaiso Morg/ne. i\(kMinooha T//JRidge. 2 —r= M/UES. Fig. 10. Map of the lower Das Plaines river, showing towns, tributaries, anddistribution of drift. Rv, Riverside ; S, Summit; Wi, Willow Springs; Lm, Lemont;Ro, Romeo; Lk, Locliport; J, Joliet; N. L, New Lenox ; C. Cliannahon ; Wh,Wheaton; Na, Naperville; Au, Aurora; 1, Salt creek; 2, Chicago river; 3, Flagcreek ; 4, Calumet river ; 5. Long run ; 7, Fraction run ; 8, Spring creek ; 9, Hickorycreek; 10, Sugar creeli; 11, Jackson creek; 12, Prairie creek; 13, Rock creek; 14,Dupage river; 15, Ausable creek: 16, Fox river; 17. Buffalo creek; 18, Isle laCache creek; 19, Mink creek; 20, Crystal run. Drift plotted from U. S. Geol. Surv.,Monog. 38, by Leverett, with minor changes. shown on the sketch ma]D (Figure G). Its ]30sition is marked out by thebroad Shelb3-ville moraine, a continuous belt of drift built up alongthe ice margin,, when, for a considerable time, the backward melting
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